Endocrine and molecular regulation mechanisms of follicular development and egg-laying in quails under different photoperiods.

Photoperiod is a key environmental factor in regulating bird reproduction and induces neuroendocrine changes through the hypothalamic-pituitary-gonadal (HPG) axis. OPN5, as a deep-brain photoreceptor, transmits light signals to regulate follicular development through TSH-DIO2/DIO3. However, the mechanism among OPN5, TSH-DIO2/DIO3, and VIP/PRL in the HPG axis underlying the photoperiodic regulation of bird reproduction is unclear. In this study, 72 laying quails with 8-week-old were randomly divided into the long-day (LD) group [16 light (L): 8 dark (D)] and the short-day (SD) group (8 L:16 D), and then samples were collected on d 1, d 11, d 22, and d 36 of the experiment. The results showed that compared with the LD group, the SD group significantly inhibited follicular development ( < 0.05), decreased the P4, E2, LH, and PRL in serum ( < 0.05), downregulated the expression of , , , , and ( < 0.05), reduced the expression of and ( > 0.05), and promoted gene expression ( < 0.01). The short photoperiod downregulates , , and and upregulates expression to regulate the GnRH/GnIH system. The downregulation of and upregulation of resulted in a decrease in LH secretion, which withdrew the gonadotropic effects on ovarian follicles development. Slow down of follicular development and egg laying may also arise from lack of PRL potentiation to small follicle development under short days.